Hydraulic excavators are featured with wide application range, large energy consumption, and strong periodicity in operation. Energy-saving technology researches for hydraulic excavators have great economic value and feasibility. When a traditional hydraulic excavator is in rotatory start and deceleration braking, the rotatory start and deceleration braking torque is determined by an overflow pressure that is set by the rotatory overflow valve. During the rotatory start process, because the flow rate provided by the hydraulic pump is greater than the flow rate needed by the rotary motor, overflow loss from the rotatory start may be generated. During the rotatory deceleration braking process, because the deceleration braking effect is achieved by a deceleration braking torque produced by a reversing back pressure of the rotatory overflow value, overflow loss from the rotatory deceleration braking may be generated. The overflow oil may produce a large amount of heat energy, which heats the hydraulic system of the excavator, and reduces performance and lifetime of the hydraulic system. Since the excavator operation has strong periodicity characteristics, the rotatory action may be much frequently performed. This causes severe energy loss. If the energy loss can be recycled and reused, considerable economic benefits can be obtained.
Chinese patent application No. CN101736771 A discloses a rotatory deceleration braking energy recycling system of a hydraulic excavator. Such energy recycling system only recovers overflow energy from the rotatory deceleration braking, and does not recover overflow energy from the rotatory start. Chinese patent application No. CN 102733442 discloses a hydraulic excavator rotatory energy recycling system of a hydraulic excavator. Such system uses a three-position three-way directional valve to respectively recycle energy from a forward rotation and a reverse rotation. However, the response time of the directional valve may affect energy recycling and the rotation performance. There are also some devices that create back pressure during energy recycling, by using an energy storage device such as an energy accumulator, or using an energy utilization device such as a hydraulic motor. However, the back pressure created in this manner is unstable and affects performance of the rotatory system of the hydraulic excavator.